1. Field of the Invention
The present invention relates generally to a mandrel extractor system for a mandrel of a tube bending machine, and more particularly, to a mandrel extractor system which advances and retracts the mandrel at pre-programmed pressure levels.
2. Description of Related Art
Tube bending machines are well-known in the art. In one common type of machine, a tube is secured between a bend die and a clamp die which rotate together, drawing the lead portion of the tube therewith to bend it around the bend die. A pressure die engages an outside wall of the trailing portion of the tube to counter the reaction force of the tube during the bending operation.
Some machines place a mandrel within the tube so that as the tube is drawn over the mandrel as the tube is being bent (i.e. as the bend and clamp dies are rotated) the mandrel helps maintain proper cross-sectional configuration of the tube throughout the bend. Mandrels are particularly important in bending relatively thin walled tubes. Some mandrels are flexible, such as having multiple balls linked together, so that the mandrel can be extended beyond the tangent point of the tube and the bend die to still further ensure maintenance of the proper cross-sectional configuration of the tube throughout the bend.
The mandrel is typically connected by a mandrel rod to a mandrel extractor which is mounted at the end of the machine bed. The mandrel rod is moved back and forth by the hydraulic mandrel extractor to push the mandrel inside the tube during a bend operation and to extract the mandrel from the tube after the bend operation. Conventional mandrel extractors drive and extract the mandrel under constant pressure, and typically at a high system pressure of the tube bending machine. One problem with a constant pressure system, however, is safety of operating personnel. When the mandrel is pushed at a relatively high system pressure, the long thin mandrel rod can buckle and ultimately break. Striking any obstruction while moving the mandrel rod at a high pressure can cause the rod to jam and break and possibly swing around at a high force. Another problem with constant pressure systems is that the mandrel often cannot be extracted from the tube after the bending operation because the pressure is not high enough. Accordingly, there is a need in the art for an improved mandrel extractor which reduces breakage of mandrel rods and/or improves removal of the mandrel from the tube after the bending operation.